DESCRIPTION: The broad, long-term objectives of the proposed research are to understand the regulatory mechanisms underlying physiological changes which cells undergo in response to decreasing availability of nutrients. The work will be carried out using the well-studied bacterium Escherichia coli since much has already been learned about how this simple organism adapts to conditions of starvation. Since microbial growth is usually limited by the availability of essential nutrients, knowledge gained from the proposed studies will have general implications to our understanding of the molecular mechanisms that allow microbial survival in the natural environment. Upon the onset of starvation E. coli initiates a developmental program that results in a much smaller and more resistant cell. These changes are brought about by a dramatic switch in the pattern of gene expression. Under many conditions of starvation this switch in gene expression is mediated in part by the production of a new sigma factor, sigma s, which directs RNA polymerase to transcribe a new set of genes. While much is known about the induction of gene expression by sigma s in response to starvation, much remains to be understood about other aspects of starvation physiology. Our proposed studies will address three important questions on this topic which have remained relatively unexplored: How do cells sense nutrient depletion and how is that signal transduced to eventually obtain an increase in sigma s activity? How are genes which are normally expressed during growth "turned off" during starvation? What cellular functions are induced only after cells have been starved for extremely long times? These questions will be addressed by using a combination of genetic, biochemical and physiological approaches.